Final answer:
Two-factor authentication (2FA) or multi-factor authentication (MFA) is a security measure that adds an extra layer of protection to online accounts by requiring users to provide two or more pieces of evidence to verify their identity.
Step-by-step explanation:
Two-factor authentication (2FA) or multi-factor authentication (MFA) is a security measure that adds an extra layer of protection to online accounts. It requires users to provide two or more pieces of evidence to verify their identity, such as a password and a fingerprint, or a password and a one-time access code sent to their phone.
Two-factor authentication is useful because it significantly reduces the risk of unauthorized access to accounts. Even if someone manages to obtain a user's password, they would still need the second factor to gain entry. This makes it much harder for attackers to compromise accounts, as they would need to have both the password and the second factor.
For example, let's say you have enabled two-factor authentication for your email account. When you log in from a new device, you will be prompted to enter a verification code that is sent to your phone. Even if someone knows your password, they won't be able to log in without the verification code.